In order to treat a blood vessel (vasculature) abnormally narrowed by arteriosclerosis or the like, percutaneous transluminal coronary angioplasty (PTCA) is applied wherein a catheter having a dilation body at a distal end portion thereof is inserted into a stenosed site and the dilation body is inflated to expand the stenosed site thereby to improve the peripheral blood flow. This technique is carried out generally in the following manner. In particular, before a catheter with a dilation body (balloon catheter) is inserted into a blood vessel, a guiding catheter for introducing the catheter with the dilation body to the stenosed site is indwelled in the blood vessel. Then, the catheter with the dilation body is inserted through a Y connector which is a medical connector connected in advance to a proximal end portion of the guiding catheter.
A conventional Y connector includes a connector main body in which a lumen is provided into which the catheter with the dilation body can be inserted, and a branch which branches from a side face of the connector main body and has a side port provided at a distal end thereof. The branch is provided integrally with a body portion of the connector main body. At one end of the connector main body, a connection portion configured for connection to a proximal end portion of a guide catheter is provided for rotation around an axial line of the connector main body. At the other end of the connector main body, a cap portion rotatable around the axial line with respect to the connector main body is provided. Between the cap portion and the connector main body, a valve body is provided. The valve body is configured from an elastic member whose inner diameter varies in response to pressure applied thereto between the cap portion and the connector main body to open or close the lumen (refer to, for example, Japanese Patent No. 4472310).